# I’m ‘not in’ right now…

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Checking whether an item is in a vector or not in a vector is a common task. The notation in R is a little inelegant when expressing the “not in” condition since the negation operator (`!`

) is separated from the comparison operator (`%in%`

):

`5 %in% c(1, 2, 3, 4, 5) # TRUE`

`!5 %in% c(1, 2, 3, 4, 5) # FALSE`

R is a language where you can easily extend the set of built in operators:

``%!in%` <-`

` function(needle, haystack) {`

` !(needle %in% haystack)`

` }`

Now, I can express my intentions reasonably clearly with my new, compact, infix operator `%!in%`

:

`5 %in% c(1, 2, 3, 4, 5) # TRUE`

`5 %!in% c(1, 2, 3, 4, 5) # FALSE`

Moral: bend your tools to your will, not the other way ’round.

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